Electromagnetic Interference (EMI) involves the introduction of unacceptable amounts of electromagnetic energy into an environment due to the presence of electrical devices and equipment. For example, a desktop or a laptop computer chassis may include many micro-electronic components that perform various electrical-based tasks. In such devices, electromagnetic energy is typically radiated due to the electrical switching operations of the components. Accordingly, the radiated electromagnetic energy may significantly degrade the performance of other devices, if the radiated electromagnetic energy is permitted to be introduced into a common environment.
EMI is physically related to the transmission and reception of electromagnetic energy. The radiation of the electromagnetic energy to the receiver may cause the receiver to act in an undesired and often unpredictable manner. EMI shielding is often utilized to reduce or eliminate the effects of EMI. Such shielding involves the placement of an electromagnetic shield or EMI shield between an EMI source and potential EMI receivers. The electromagnetic shield may be provided in the form of a continuous metal sheet. The electromagnetic shield may adopt alternative forms such as a perforated metal sheet that permits thermal radiation. The electromagnetic energy emitted by a source propagates as an electromagnetic wave. The electromagnetic wave is partially absorbed by the EMI shield. Accordingly, the intensity of the electromagnetic wave can be attenuated or reduced and the EMI effects upon receivers are lessened.
The design of an electromagnetic shield significantly impacts its effectiveness in reducing the intensity of the electromagnetic wave associated with the EMI. For example, a gap or seam in an electromagnetic shield can result in EMI leakage. Another problem associated with sheet metal EMI shields is that such components cannot easily accommodate different separation tolerances and minimum compression requirements throughout the EMI shield. Accordingly, EMI gaskets are utilized to prevent gaps or seams from causing EMI leakage. EMI gaskets are conductive media designed to provide for a flexible connection between two electrical conductors used as EMI shields.
EMI gaskets can be selectively placed to reduce any slots, seams, or other discontinuities between the EMI shields to prevent EMI leakage. EMI gaskets are used to maintain shielding effectiveness by proper seam treatment. It is the effect of these seams and discontinuities, in general, which accounts for most of the leakages in an enclosure design. The shielding effectiveness of a seam is dependent upon the materials, contact pressure, and surface area. Deviation from the appropriate compression force may either allow EMI leakage or damage the EMI gasket.
In an effort to address the foregoing difficulties, a continuous metal to metal contact can be provided using a valley feature on one side of EMI gasket and a crown feature on the opposite side that complements the valley. It is believed that the implementation of such a method can reduce EMI leakage and maintain a good EMI grounding.